The acidic proline-rich proteins (PRPI, PRPII, PRPIII and PRPIV) constituting a major group of salivary proteins in parotid and submandibular secretions are known to display important functions in the oral cavity. First, these proteins have been shown by electrophoretic and chromatographic techniques and recently in our laboratory by the indirect immunoperoxidase method to be precursor molecules of the acquired enamel pellicle. Secondly, the acidic proline-rich proteins play an important role in maintaining the state of calcium phosphate supernaturation with respect to hydroxyapatite in saliva by acting as inhibitors of calcium phosphate precipitation. Thirdly, these proteins exhibit certain similarities with structural proteins such as enamel matrix proteins and have been shown to play a role in de- and remineralization processes on the tooth surface. Recent efforts led to the isolation and characterization of a proline-rich protein (MPRP), from parotid saliva of the primate Macaca fascicularis, which exhibits immunological cross-reactivity and considerable amount of sequence homology with the human acidic proline-rich proteins. The work proposed in this application makes use of this unique animal model system to study the subcellular localization of MPRP in glandular tissue by immuno-histochemical labelling techniques at the E.M. level and the regulation of secretion of these proteins in an in vitro slice system. For this purpose, a radioimmunoassay system will be developed which will in addition, lay the ground work to probe the quantitative relationships of the acidic proline-rich proteins in various secretions and pellicle.